Metallizing nonmetallic bodies



deposition.

Patented Nov. 11, 1947 PATENT OFFICE METALLIZIVNG NONMETALLIC BODIESLeopold Pesscl, Philadelphia, Pa., assignor to Radio Corporation ofAmerica, a corporation of Delaware g No Drawing. Application November29, 1944, Serial No. 565,815

14 Claims.

This invention relates to a method of metallizing non-metallic bodies,and more particularly to a method of chemically depositing metallicnickel, metallic cobalt or mixtures of these two metals onnon-conductive surfaces whereby to provide firmly adherent, hard,tarnish resistin metallic films having good electrical conductivity.

In the metallization of non-metallic bodies, it has been customary, inthe past, to first produce a metallic film thereon by one of severalmethods, such as evaporation, metal spraying or chemical The last namedmethod has often been preferred because of the ease with which a largevariety of non-metallic bodies can be metallized thereby. However, forall practical purposes, only silver has been used for such chemicaldeposition. Several methods of producing such silver films areavailable, among these being the Brashear method, the Rochelle Formulamethod, etc. These are all based on chemical reduction from anammoniacal silver solution and are subject to certain shortcomings whichare more or less common to all of them. For example, the solutions arelight-sensitive and their performance is easily affected by the presenceof certain impurities such as chlorides. Under certain conditions, theyare prone to produce deposits of a silver-nitrogen compound which hasexplosive characteristics. The solutions cannot be stored indefinitelyand, if stored at all, this must be done in cool, light protectedplaces.

Other disadvantages pertain to the silver films produced by thesemethods. For one thing, the film is soft and does not show muchresistance against abrasion. It is subject to tarnish which isparticularly serious in an atmosphere containing sulphur compounds. Thistarnish is often sufficiently heavy to offset the advantage of highelectric conductivity which the films possess initially. Finally, undercertain conditions, the silver film is subject to-a form of dendriticgrowth which is particularly harmful in the 'case of quartz plateoscillators which are silver-plated by chemical deposition.

Films of other metals, particularly gold, copper, and the platinummetals, have also been produced by chemical reduction. In the case ofcopper, the tarnishing characteristics are even more pronounced thanwith silver, while gold is even softer than silverand the platinummetals. In any case, the depositions of the latter metals by chemicalreduction to provide satisfactory films is a very expensive process. I

I have found that satisfactory films consisting of metallic nickel,metallic cobalt,.or mixtures of these two metals can :be produced bychemical reduction and applied to non-metallic bodies or surfaces in avery effective manner and that the films produced according to mypresent invention 5 will not only adhere firmly to such bodies orsurfaces but will be hard and tarnish resistant and will have very goodelectrical conductivity. The process of my present invention readilylends itself to the chemical deposition of nickel,'cobalt, and mixturesthereof on such non-metallic bodies as quartz, glass, ceramics, mica,plastics and the like.

Now, it hasv been known for sometime that metallic nickel or cobalt canbe obtained from The primary object of my present invention is toprovide an improved method of depositing metallic nickel, cobalt, and/ormixtures thereof upon non-metallic bodies, which method will be entirelyfree from the aforementioned limitations.

More particularly, it is an object of my present invention to provide animproved method of depositing the aforesaid metals which can be carriedout rapidly and at room temperatures.

Another object of my present invention is to provide an improved methodas aforesaid which will produce films of metallic nickel, cobalt and/or0 mixtures thereof which will be low in phosphide content and which willhave good electrical conductivity.

Still another object of my present invention is to provide an improvedmethod of depositing the aforesaid metals in a manner which will provideuniform films on the surface of any nonconductive object immersed in theplating solution from which the metal is deposited.

A further object of my present invention is-to 0 provide an improvedmethod as aforesaid which will result in films upon which the same orother metals can be electrodeposited with great efiicacy.

Still a. further object of my present invention is to provide improvedcoatings of metallic nickel,

cobalt and/or mixtures thereof upon non-metallic an aqueous solution oftheir salts by the reducing bodies, which coatings will have suchproperties from the standpoints of adhesion, hardness,tarnish-resistance and electrical conductivity as to render them usefulin combination with such non-metallic bodies as piezo-electric quartzcrystals, glass, mica, ceramics, plastics and other similar materialswhereby to obtain novel forms of electrical and other useful articles,such as quartz plate oscillators, electric capacitors, electriccontacts, matrix shells and many other devices.

Another object of my present invention is to provide on non-metallicsurfaces adherent metal coatings or films as aforesaid to which solderjoints may be readily made by hot-tinning or hotsoldering.

It is also an object of my present invention to provide an'improvedmethod of depositing metallic nickel, cobalt and/or mixtures thereofwhich can be readily carried out with great efficiency even by one nothighly skilled in the art, and which is relatively inexpensive topractice.

In accordance with my present invention, I effect the deposition of thenickel, cobalt, or mixtures thereof chemically from a bath containing ahypophosphite, a hydrazine compound, and a noble metal catalyst. Theresulting film or coating may be used directly as an electricalconductor or for any other suitable purpose, such as a base for a solderconnection, as a base for subsequent electrodeposition of the same orother metals, or for other similar purposes, as may be desired.

The reduction of a nickel or cobalt salt by means of hypophosphite inthe presence of a noble metal catalyst takes place rather slowly at roomtemperature. Hydrazine, too, in the presence of a similar catalyst, hasan extremely slow reducing action at room temperature. I, have found asurprising acceleration of the reducing action if the solutions, inaddition to the catalyst, contain simultaneously a hypophosphite and ahydrazine compound. The acceleration is so 4 If the hypophosphite isleft out of this mixture, leaving only the hydrazine hydrate and thePdClz to react with the nickel acetate, no reaction or film formationwhatever is noted after 10 minutes at room temperature.

I have also found that not all nickel salts are reduced with the samerapidity and that there exists a definite influence of the anion uponthe reducing action. Thus, the acetate appears to work better than thechloride, and the latter better than the sulphate. However, outstandingperformance is obtained in the presence of the formate ion. This may beintroduced either by using nickel formate, or by the addition of someother soluble formate, such as sodium formate. Good reduction is alsoobtained in the presence of ions of a hydroxy acid, other than tartaricacid, such as citric or lactic acid, or of a keto acid, such aslevulinic acid. These ions may be introduced by the USQ'Of thecorresponding nickel or cobalt salts, or by the addition of some solublesalt of these acids.

eat that reduction and film formation occur within a few minutes notonly at room tempera- NiSO43N-2H4, C0Cl22N2H4, COSO4-3N2H4, etc. It islikely that the formation of such double salts or addition productscontributes to the effect observed. In any case, this effect is verystriking.

For instance, if, to the mixture No. 1 given below, 2 drops of a 0.1%PdClz solution are added, intensive reaction sets in at room temperatureafter several minutes. After 10 minutes, the reaction is practicallycompleted and the walls of the glass vessel containing the mixture arecovered with an opaque, nickel mirror having an electrical resistance ofabout 300 ohms between two points 1 cm, apart. However, if the hydrazinehydrate is left out of this mixture, the reaction is much slower at roomtemperature. After 10 minutes, no mirror is obtained but only a veryfaint dark film having an electrical resistance of the order of 10 ohmsbetween two similar points.

The electrical conductivity of the films obtained by the reactiondepends partly upon the phosphite content of the deposits. The P contentmay be as high as 13-14%, resulting in relatively poor electricalconductivity. However, films obtained by the method described hereinhave a much lower P content, this being of the order of 3% or even less.Films of lower P con tent are obtained by increasing the alkalinity ofthe solutions, as by the addition of ammonia. However, even betterresults may be obtained by the use of organic nitrogen-containing baseswith at least one C-N bond. Such bases may be of the amine type, such asmonoethyl-amine or diethyl-amine; of the heterocyclic type, such asmorpholine or pyridine; or of the quaternary ammonium base type, such astetraethanol ammonium hydroxide or benzyl trimethyl ammonium hydroxide.An additional advantage of introducing such basic substances lies intheir surface tension decreasing and detergent action which aids in theformation of more uniform films having improved adhesion.

In a similar manner, benefits may be obtained by the addition of othermaterials which, while not alkaline in nature, act as solvents orwetting agents, Such materials may be water soluble organic solvents,such as ethyl or methyl alcohol, acetone, dioxane, diethylene glycol,monoethyl ether acetate, acetonyl acetone, propylene oxide, glycoldiformate, etc. They may also be highmolecular weight wetting agents, ofwhich a large number are known. Characteristic examples are a sorbitanmonolaurate polyoxyalkylene derivative made by the Atlas Powder Co.,Wilmington, Del., an aryl alkyl polyether alcohol made by Rohm and HaasCo., Philadelphia, Pa., acetyl dimethyl benzyl ammonium chloride (alsomanufactured by Rohm and Haas C0,), etc. All of the wetting agentsuseful for this purpose have at least one chain of not less than 6 Catoms.

The improvements described above apply to the formation of both nickeland cobalt films. In addition, I have been able to obtain filmscontaining .both nickel and cobalt with a varying small amount ofphosphorus. Metallic films containing both nickel and cobalt have beenobtained previously by electrodeposition and such films aredistinguished by superior hardness and corrosion resistance. The filmsobtained by the simultaneous chemical deposition of nickel and cobaltshow the same advantages together with some additional ones based uponthe extremely fine grain of chemically deposited layers and the smallphosphide content. These factors are particularly important with respectto adhesion to certain non-metallic surfaces. I have preferred to useequal weight percentages of both nickel and cobalt salt in the reducingsolution. However, other relative proportions may be used.

The solutions described may be prepared in any convenient manner and maybe stored for considerable periods without deterioration, especially ifkept in a refrigerator. However, it is advisable to prepare thehypophosphite solution separately and to add it to the mixture of theother ingredients shortly before the solution is to be used.

In order to start the reaction, addition of an accelerating catalyst isnecessary. This catalyst is best chosen from the family of the platinummetals and may consist of. a solution of a platinum salt, palladiumsalt, etc. The concentration of such a solution may be varied over awide range, the reaction taking place more quickly if higherconcentrations are used. I prefer to use a 0.1% solution of palladiumchloride in water, of which I add 1 or 2 drops for each cc. of reducingsolution used.

The action of thecatalyst is presumably due to the reducing action ofnascent hydrogen adsorbed on the colloidal palladium. In order to obtainuniform film formation, it is important that the colloidal catalystremain in contact with the surfaces to be metallized and that it beprevented from precipitating and settling prematurely to the bottom ofthe reaction vessel. I have found it advantageous to add a protectivecolloid to the solution of the catalyst. This may be done by adding asmall percentage of a colloidal material such as polyvinyl alcohol,methyl cellulose, glue, etc. to the palladium solution. It is alsoadvantageous to keep the solution in motion by'mechanical stirring. orto introduce bubbles of air or some other gas while the film formationtakes place.

In giving below a number of solutions representing various embodimentsof my invention, I wish to emphasize that this invention residesprincipally in the qualitative composition of the solutions used. Thequantitative relation, i. e., percentage of the various ingredients, maybe varied over a wide range between extreme dilution and saturation ofthe solution with any particular ingredient. The actual quantity of theingredients is thus amatter of choice-governed by practicalconsiderations, such as the preferred reaction speed, and byconsiderations of economy with respect to the cost of the ingredientscontained in the spent solution. I have preferred to use solutions ofthe indicated concentrations, although higher or lower concentrationsmay be used. The solutions described are intended only as examples andillustrations of the principles of the invention but not as limitationsas to quantitative composition. Neither should the descriptionbeconstrued as a limitation excluding the use of compounds of a closelyrelated chemical nature.

The percentages indicated in the following illustrative compositions arebased onweight in aqueous solution, while the figures indicate volumeparts:

1% nickel acetate 10 Saturated solution of sodium hypophosphite 1 85%hydrazine hydrate 1 1% nickel formate 10 Saturated solution of sodiumhypophosphite 1 85% hydrazine hydrate 1 1% nickel levulinate 10Saturated solution of sodium hypophosphite 1 85% hydrazine hydrate 1 1%nickel formate 10 Concentrated aqua ammonia 1 Saturated solution ofsodium hypophosphite 1 85% hydrazine hydrate 1 1% nickel citrate 10Saturated solution of sodium formate 1 Saturated solution of sodiumhypophosphite 1 85% hydrazine hydrate 1 6 l 1% nickel formate 10Saturated solution of sodium hypophosphite 1 Concentrated aqua ammonia 3Solid hydrazine sulfate 5% of total 1% nickel acetate 10 Saturatedsolution of sodium hypophosphite 1 85% of hydrazine hydrate 1 Methanol 38 1% nickel acetate 10 Saturated solution of sodium hypophosphite 1 85%hydrazine hydrate.. 1 Sorbitan monolaurate polyoxyalkylene derivative 2%of total 1% nickel formate 10 85% hydrazine hydrate l Saturated solutionof sodium hypophosphite 1 42% benzyltrimethyl ammonium hydroxide 1 1%cobalt acetate 10 Saturated solution of sodium hypophosphite 1 hydrazinehydrate 1 1% cobalt acetate 10 Concentrated aqua/ammonia 1 Saturatedsolution of sodium hypophosphite 1 85% hydrazine hydrate -1 1 1% cobaltacetate 10 1% nickel formate 10 Saturated solution of sodium hyD phosP t2 85% hydrazine hydrate 2 place and the remainder of the reactionconsists primarily in hydrogen evolution, the objects may be removed,washed in water or any other desired medium and dried by any convenientmethod. On the other hand, if a thicker film is desired than can beobtained by one reaction stage, the bodies may be reimmersed into asecond bath directly after removal from the first bath and the procedurerepeated. This may be done any desired number of times.

I have also found that such films constitute an excellent electricallyconductive base for the subsequent electrodeposition of other metals,such as copper, nickel, silver, gold, etc., and that the combination ofsuch electrodeposited metals with chemically deposited nickel or cobaltpossesses novel and meritorious qualities with respect to adhesion,electrical conductivity and other properties.

The films can be readily coated with molten tin, solder, or similaralloys by any of the customary soldering procedures and such acombination provides excellent means of makin solder connections withthe non-metallic base carrying the film. The hot-tinning operation maybe carried out directly on the chemically deposited nickel or cobal't bythe use of a special flux, such as an organic phosphate or pyrophosphate(for instance, isopropyl acid pyrophosphate in alcoholic solutions) orthe chemically deposited film may be electroplated with an easilysolderable metal such as copper, tin, silver, cadmium, etc. and thehottinning operation carried out without flux or with the aid of a mildflux, such as rosin. In some cases, particularly if the non-metallicbase is heat sensitive, solder alloys of lower melting point, such asthose containing lead and bismuth may be used.

The present invention has been utilized with particular success in theformation of metal electrodes on quartz oscillator plates useful inradio circuits. Such electrodes have heretofore been produced bychemically depositing silver films. Such silver films, however, are softand subject to tarnishing and to a dendritic crystal growth under theinfluence of an applied D. C. potential tending to produce a shortcircuit around the edges of the oscillator plate. Nickel or cobalt filmsdeposited by the method described herein were found to possess excellentadhesion to the quartz and t show considerable hardness and resistanceagainst tarnishing. They were free from dendritic growth. Where the filmformed in one plating step was of insufficient thickness, two such stepswere used successively, Another type of electrode may be produced byfirst metallizing the oscillator plate with nickel, cobalt or both ofthese metals by chemical deposition according to the present inventionand then applying a layer a of electrodeposited nickel.

Another application of the invention lies in the formation of theconductive layers of condensers. The dielectric in this case may bemica, glass, paper, plastic material, ceramic material, etc. In thiscase, too, the chemically deposited film may be used alone or incombination with a subsequently electrodeposited metal.

Still another application lies in the metallization of materials such aswax, shellac, ethyl cellulose, cellulose acetate, etc, for the purposeof producing matrix shells by subsequent electrodeposition of copper orsome other metal and separating the metallic layer from the non-metallicbase. i

Still another application lies in the metallization of plastic such asBakelite, methacrylate, polystyrene, etc. for the purpose of producinelectrically conductive films or optically reflective mirrors. Many suchapplications in the field of electronics will suggest themselves.

Another application lies in the formation of hermetic seals joiningnon-metallic bodies, such as glass bushings, to metallic housings. Forapplications of this type, it is advantageous to heat the metallizedbody to an elevated temperature, preferably in a protective atmospheresuch as hydrogen or nitrogen gas. The metallized glass bushing is heatedto a temperature substantially above C. but below the fiow point of theglass. After cooling, the metallized layer may be hot-tinned andsoldered by the method outlined above.

From the foregoing description, it will be manifest that I have providednot only an improved method of producing films of nickel, cobalt, andmixtures of these two metals by chemical deposition, but also novelcombinations of such layers with metallic films produced by othermethods and with non-metallic materials. Due to the uniquemicrostructure and composition of the chemically deposited layers, theaforesaid combination possess novel characteristics unobtainedheretofore. It will be evident that many changes, modifications, andcombinations of the matter described above can be made on the basis ofthe facts established, and it is therefore desired that the inventionshall not be limited except insofar as is made necessary by theprior'art and by the spirit of the appended claims.

What is claimed is:

l. The process of metallizing a non-metallic body which comprisesimmersing said body in a solution containing a, salt of a metal selectedfrom the group consisting of nickel and cobalt, a hypophosphite and ahydrazine compound.

2. The process of metallizin a. non-metallic body which comprisesimmersing said body in a solution containing a salt of a metal selectedfrom the group consisting of nickel and cobalt, a hypophosphite, ahydrazine compound, and a. compound of a member of the group of platinummetals.

3. The process of metallizing a non-metallic body which comprisesimmersing said body in a solution containing a salt of a. metal selectedfrom the group consisting of nickel and cobalt, a hypophosphite, ahydrazine compound, ammonia, and a compound of a member of the group ofplatinum metals.

4. The process of metaliizing a non-metallic body which comprisesimmersing said body in a solution containing a salt of a metal selectedfrom the group consisting of nickel and cobalt, a hypophosphite, ahydrazine compound, an organic base containing a C-N bond, and acompound of a member of the group of platinum metals.

5. The process of metallizing a non-metallic body which comprisesimmersing said body in a solution containing a salt of a metal selectedfrom the group consisting of nickel and cobalt, a hypophosphite, ahydrazine compound, anions of an acid selected from the group consistingof formic acid, keto acids and hydroxy acids other than tartaric acid,and a compound of a member of the group of platinum metals.

6. The process set forth in claim 1 characterized in that the solutionalso contains an organic compound selected from the group consisting ofwater-soluble alcohols, ketones, ethers and esters.

solution containing a nickel salt, a cobalt salt, a

hypophosphite, a hydrazine compound and a compound of a metal selectedfrom the group of platinum metals.

9. The process set forth in claim 2 characterized in that said compoundis one capable of precipitating out the platinum group metal to providea colloidal suspension of said metal capable of acting as a catalyst,and characterized further in that said precipitated metal is maintainedin suspension by mechanical agitation,

10. The process set forth in claim 2 characterized in that said compoundis one capable of precipitating out the platinum group metal to providea colloidal suspension of said metal capable of acting as a catalyst,and characterized further by the addition of a protective colloidcapable of maintaining said platinum group metal in colloidalsuspension.

11. The process set forth in claim 2 characterized by the additionalstep of passing bubbles of an external gas through said olution whilesaid body is immersed therein. 12. The process set forth in claim 2characterized in that said solution is maintained at a temperature notexceeding 20 C.

13. The process of metallizing a non-metallic body which comprisesdepositing on said body a metallic film by bringing it in contact with asolution containing the salt of a, metal selected from the groupcomprising nickel and cobalt, a reduc ing agent comprising a mixture ofa hydrazine compound and a hypophosphite, removing the metallized bodyfrom the solution, and heating said metallized body to a temperatureabove C. but below the fiow point of said body.

14. The process of establishing a solder connection to a non-metallicbody which comprises bringing said body into contact with a solutioncontaining the salt of a metal selected from the group comprising nickeland cobalt and a reducing agent comprising a mixture of a hydrazinecompound and hypophosphite, maintaining said contact until a metallicfilm has been formed on said body, and thereafter applying a layer ofmolten solder to said metallic film.

LEOPOLD PESSEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,448,792 Cole Mar. 20, 19232,333,534 Lang Nov. 2, 1943 2,383,311 Hein Aug. 21, 1945 OTHERREFERENCES Deutsche Chem. Gesell, Berichte, vol. 64 (J uly- Dec.) 1931,pages 1766, 1773 and 1774 of an article by C. Paul et al.

